As mobile devices have been increasingly developed and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased as an energy source for the mobile devices. Accordingly, much research on batteries satisfying various needs has been carried out.
In terms of the shape of batteries, the demand for prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, on the other hand, the demand for lithium secondary batteries, such as lithium cobalt polymer batteries, having high energy density, discharge voltage, and output stability, is very high.
One of the principal problems to be solved in connection with such secondary batteries is to improve the safety of the secondary batteries. Generally, a lithium secondary battery may explode due to high temperature and high pressure which may be induced in the lithium secondary battery due to the abnormal operation of the lithium secondary battery, such as an internal short circuit, overcharge exceeding allowable current and voltage, exposure to high temperature, or deformation caused by external impact, including dropping.
A general structure of a pouch-shaped secondary battery including a stacked type electrode assembly is typically shown in FIG. 1.
Referring to FIG. 1, the pouch-shaped secondary battery 100 is configured to have a structure in which an electrode assembly 300 including cathodes, anodes, and separators or solid electrolyte coating separators respectively disposed between the cathodes and the anodes is mounted in a pouch-shaped battery case 200 formed of an aluminum laminate sheet in a sealed state such that two electrode terminals 400 and 410 connected to anode and cathode tabs 302 and 304 of the electrode assembly 300 are exposed to the outside.
For the stacked type electrode assembly 300 as shown in FIG. 1, the inner upper end of the battery case 200 is spaced from the electrode assembly 300 such that the anode tabs 302 and the cathode tabs 304 are respectively coupled to the electrode terminals 400 and 410 by welding.
According to circumstances, a stacked/folded type electrode assembly or a wound type electrode assembly may be used in addition to the stacked type electrode assembly 300 as shown in FIG. 1.
Meanwhile, FIG. 2 is a plan view of FIG. 1 and FIGS. 3 and 4 are enlarged typical views showing part A and part B of FIG. 2, respectively.
In addition, FIG. 5 is a vertical sectional view typically showing a conventional battery cell.
Referring to these drawings, a conventional electrode assembly 300 is generally formed in a rectangular shape with the result that the distance between the electrode assembly 300 and the inside of a battery case 200 is not uniform. For this reason, there are present dead volumes S and S′ at the left and right sides and the upper and lower parts of the battery case 200.
Such dead volumes S and S′ cause deformation of the battery case 200 or the electrode assembly 300 when the battery cell 100 drops, thereby decreasing safety of the battery cell 100.
In addition, the dead volumes S and S′ reduce battery capacity of the battery cell as compared with other battery cells having the same standard.
Consequently, there is a high necessity for technology that is capable of more safely and efficiently increasing the capacity of a battery cell and securing safety of the battery cell.